1. Field of the Invention
The invention relates to a device for threading a binding thread along a transfer path extending between the thread spool and a sewing needle of a stitching unit of a thread stitching machine configured for the binding of books in sheets at the groove side thereof.
2. Description of the Related Art
Thread stitching machines of the aforementioned kind are disclosed, inter alia, in European patent documents 0 537 106, 0 603 126, 0 665 121, 0 832 758 and also in the prior art described therein.
The threading of the binding thread along the transfer path between the thread spool and the sewing needle is realized by manual labor and pincer-like auxiliary instruments across the different manipulation devices for securing the thread along the transfer path, such as, for example, the thread tension device, the thread clip, the thread length compensation device, the thread sensor, the thread tensioner and so on, which make the threading labor more difficult.
It is an object of the present invention to simplify the threading of the thread and to shorten the threading time along the transfer path and within the stitching unit of the thread stitching machine.
In accordance with the present invention, this is achieved in that the transfer path is formed by a thread guiding device correlated with at least one of the manipulation devices for guiding the binding thread and connectable to a compressed air source for the threading and/or the transport of the binding thread.
By these measures, the threading and the subsequent conveying of the binding thread on the manipulation devices and/or the sewing needles of the corresponding transfer paths is considerably facilitated.
It has been shown to be advantageous when the thread guiding device is formed by a conveying line arranged upstream of the manipulation devices and/or the sewing needle, respectively, into which conveying line at least one compressed air conduit opens which is connected to the compressed air source and positioned at an acute angle in the transport direction relative to the conveying line. This constructive measure is beneficial for the manual process of threading of the binding thread along the transfer path.
Preferably, the conveying line has a widened inlet opening and effects thereby a thread centering and makes the drawing-in action easier.
A further simplification of the threading labor can be realized when the compressed air supply can be changed by a control valve.
In connection with the threading of the binding thread into the conveying lines it is expedient when the compressed air supply to the individual conveying lines is controlled by valves.
When the individual conveying lines have a greater length, it may be expedient when several compressed air conduits are connected thereto which is beneficial with respect to the conveying action.
In a long conveying line with several compressed air conduits it is advantageous when the cross-section of the conveying line widens toward the end of the conveying path.
In the case of a conveying cross-section which tapers in the conveying direction towards the end of the conveying path, the velocity of the conveying medium can be increased.
Since the individual manipulation devices between thread spool and sewing needle can move the binding thread in the operating position into an arbitrary position which is different from the rest position, it is advantageous when the manipulation devices during threading of the binding thread are moveable into a position such that the conveying lines form in the threading or drawing direction at least substantially a straight transfer path.